This invention relates to an improved electrolyte for non-aqueous electrochemical cells, specifically of the lithium/manganese dioxide type. However, it also relates more generally to a variety of such cells of differing chemistry which may be generally characterized as having active metal anodes, active porous solid cathodes, a separator between the electrodes and a non-aqueous liquid electrolyte permeating the separator and in contact with the anode and cathode. The electrolyte includes a salt of the anode metal and organic solvents therefor.
Such cells, in hermetically sealed condition, are particularly useful as power sources for medical devices. A preferred form for such cells in medical devices includes a flat sided metal container or can. Hermeticity is achieved by welding the can closed.
In discharging such cells the cell components are known to undergo a variety of chemical reactions which cause formation of various gases such as methane, resulting in swelling of the cell container. This is particularly disadvantageous in the sealed flat sided cells preferred for medical use. Moreover, these cells have been found to lack stability at elevated temperatures, such as autoclave temperatures, and thus have not been as useful as desired for various medical applications such as powering heart pacemakers and the like. Also, it has recently been discovered that such cells undergo on discharge the formation of corrosion products at least some of which form on the anode and detrimentally affect efficiency of operation.
It is a purpose of this invention to significantly reduce each of these aforenoted negative characteristics while maintaining and even improving the desirable characteristics of these cells and providing them with longer useful lives.